Continuously variable resistance apparatus



May 23, 1961 W. L. DENISTON CONTINUOUSLY VARIABLE RESISTANCE APPARATUS Filed March 22, 1960 FIG. 4

United States Patent CONTINUOUSLY VARIABLE RESISTANCE APPARATUS William L. Deniston, Pasadena, Calif assignor to Fairchild Camera and Instrument Corporation, a corporation of Delaware Filed Mar. 22, 1960, Ser. No. 16,760

7 Claims. (Cl. 338-125) This invention relates to continuously variable resistance apparatus and, while it is of general application, it is particularly suitable for embodiment in a single revolution high resolution potentiometer and will be specifically described in such an environment.

In many electrical control systems it is desirable to provide a single revolution potentiometer which is adjustable over a wide range of resistance values, but which, at the same time, has a high resistance resolution, that is, an extremely small increment of resistance variation with incremental adjustment of the movable contact, These two characteristics are mutually incompatible in a single simple potentiometer. Heretofore, there have been proposed several types of apparatus for achieving these characteristics usually including multiple resistance elements, one with a high resistance resolution and one or more with low resistance resolutions, together with arrangeinents for repetitively traversing the element of high resistance resolution while traversing the element of low resistance resolution in steps. One such arrangement is described in US. Patent No. 2,625,632 to Onia et a1. However, such prior art apparatus have involved relatively complex electrical or mechanical interconnections, or both.

It is an object of the present invention, therefore, to provide a new and improved continuously variable resistance apparatus connected by both a wide range of resistance variation and a high resistance resolution.

It is another object of the invention to provide a new and improved continuously variable resistance apparatus of the type described which obviates the above-mentioned complex electrical and mechanical interconnection connections of prior art devices for achieving a similar result.

In accordance with the invention, an apparatus for providing a continuously variable resistance over a wide range of values comprises an elongated first resistance element having a relatively low resistance resolution and a second resistance element having a length equal to a minor fraction of that of the first resistance element and having a relatively high resistance resolution. The apparatus further comprises a contact assembly including a first contact element movable over the length of the first resistance element and a plurality of second contact elements electrically interconnected and simultaneously successively movable over the second resistance element, the contact elements being effective to connect the two resistance elements in series, whereby the apparatus has an effective resolution over its entire range of values equal to that of the second resistance element. The term elongated resistance element refers to a resistance element, either continuous in length or made up of a plurality of discrete resistance elements serially connected in an elongated string and in which the elongation is either rectilinear, circular, or of other linear configuration,

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection 2,985,859 Patented May 23, 1961 "ice with the accompanying drawings, while its scope will be pointed out in the appended claims.

Referring now to the drawing:

Fig. 1 is a plan view of a resistance apparatus embodying the invention; I

Fig. 2 is a cross-sectional view of the Fig. 1;

Fig. 3 is a perspective view of the rotor of the apparatus of Figs. 1 and 2, while Fig. 4 is a simplified schematic diagram of the resistance apparatus.

Referring now to Figs. 1, 2, and 3 of the drawings, there is illustrated an apparatus for providing a continuously variable resistance over a wide range of values and comprising a supporting base 10 of insulation material, such as a suitable plastic. Disposed on the base 10 is an elongated first resistance element 11 having a relatively low resistance resolution. The element 11 may be a conventional circular wound-wire resistance element including a plurality of serially-connected sections formed by bringing out a series of taps 11a, 11a provided with a plurality of segmental contact elements 12, 12 individually connected to the taps 11a, 11a. The ends of the winding 11 are brought out to terminals 2 and 3 by means of leads 11c, 110.

The resistance apparatus further includes a second resistance element 13 having an efiective electrical length equal to a minor fraction of that of the resistance element 11 and having a relatively high resistance resolution. As shown in Fig. 1, the efiective electrical length apparatus of of the winding 13 is only that portion between the taps 13a and 13b, this portion of the winding being electrically disconnected from the remainder of the winding 13. The taps 13a, 13b are brought out to terminals 1 and 4, respectively, as shown. However, the winding 13 is preferably constructed in the form of a circular woundwire resistance element concentric with the resistance element 11 and preferably having an over-all length mechanically equal to that of the resistance element 11 but an effective electrical length between the taps 13a and 13b equal to the distance between adjacent ones of the contact elements 12, 12 of the resistance element 11. The term electrical length is measured either in terms of angular distance, in the case of the circular resistance elements shown, or in terms of linear distance, in the case of rectilinear resistance elements. By making the resistance element 13 in the form of a full circle rather than a short segmental section and electrically disconnecting the unwanted portions, it has been found that it is easier to manufacture than to form only the short wanted section. Furthermore, the provision of the full circular resistance element 13 provides mechanically a uniform continuous contact surface for the contact elements 20, 20.

The resistance values of the elements 11 and 13 are proportioned so that the resistance value of the portion of the element 13 between the taps 13a and 13b is equal to the resistance resolution of the resistance element 11; that is, it is equal to the resistance between the adjacent contacts 12, 12, in the form illustrated, or the resistance between adjacent turns, in case the contact assembly described hereinafter makes contact directly with the resistance element rather than with the auxiliary contact segments.

The resistance apparatus of the invention further includes a contact assembly relatively rotatable with respect to the resistance elements 11 and 13 and including a first contact element, movable over the length of the resistance element 11, and a plurality of second contact elements electrically interconnected and simultaneously successively movable over the active portion of the resistance element 13. Specifically, the contact assembly includes a rotor 14 in the form of a circular disc of insulation material, such as a suitable plastic, secured to a hub 15, also of insulation material, as by the machine screws '16. The hub 15 is provided with an annular groove 15a in which is disposed a pair of annular rings 17 and 18 embracing opposite sides of an enlarged central aperture of the supporting base 10 and serving to journal the rotor disc 14 on the supporting base it). A dust ring 2 3 surrounds the rotor 14 and is secured to thebase 10 to protect the resistance elements 11 and 13, .and their associated contacts, described hereinafter, from dirt and extraneous objects.

. As best shown in Fig. 3, on the face of the rotor 14, adjacent the supporting base 10, is a peripheral strip 19 .of conductive material to which are secured and electrically connected a series of spring contact elements 20, 20 equal in number to the number of sections into which the resistance element 11 is divided. To the same face of the rotor 14 is secured a spring contact element 21 .electrically connected by a conductive strip 22 to the .strip 19., The disposition of the contact elements 20 [and "21 on the rotor 14 is such that the elements 20 traverse the resistance element 13 while the contact element 21 traverses the contact segments 12, 12. That is, .the contact element 21 efiectively jsmovable over the length of the resistance element 11 in a series of discrete steps as it traverses the series of contact segments 12, 12.

In the event that the design is such that the contact element 21 traverses the resistance element 11 directly, it would do so continuously from turn to turn.

Fig. 4 is a schematic diagram of the resistance apparatus of Figs. 1, 2, and 3, from which it is seen that the portion of the resistance element, 13 between the taps 13a and 13b is electrically connected in series with a 1 portion of the resistance element 11 and that this series connection is made by virtue solely of the contact of the elements 20 with the active section of the resistance element 13 and of the single contact 21 with the contact segments 12 and without the aid of any additional brushes or sliding contacts.

In explaining the operation of the resistance apparatus described above, it may be assumed that the contact elements 20, 20 and 21 are initially in the positions shown in Fig.4. Under these conditions, the resistance between the terminals 1 and 3 is the sum of the resistances of the active section of element 13 and .the'portion of the resistance element 11 to the left of the contact element 21. As the rotor is adjusted to move the contacts 20, 20'and 21 to the left, a progressively decreasing portion of the section of the resistance element 13 is included in the circuit until the contact elements 20 move a distance equal to the electrical length of the active section of the resistance element 13, during which time the contact element 21 engages the same contact segment 12. At the conclusion of this movement, the contact element 21 engages the next contact segment 12 to the left, which would be effective to decrease the total resistance by the value between adjacent contact segments. However, one of the contact elements 20 has just left the left-hand terminal of the active section of resistance element 13 and the next contact element has just engaged the righthand end of this section, again introducing the resistance value of this section into the series circuit. Since the resistance value of this active section of the element 13 is equal to that of each section of the element 11, the total series resistance of the circuit described is momentarily unchanged. As the rotor is moved progressively in a direction corresponding to the movements of the contacts 20,20 and 21 to the left in Fig. 4, the abovedescribed cycle'is repeated and the resistance value between the terminals 1 and 3 is progressively and uniformly decreased. As a result, the resistance apparatus as a whole has an effective resolution over the entire range of resistance values of the element 11 equal to the high resolution of the active section of the resistance element 13. Obviously the value of the resistance between terminals 4 and 2 varies in a sense equal and opposite to that between the terminals 1 and 3.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. Apparatus for providing a continuously variable resistance over a wide range of values comprising: an elongated first resistance element having a relatively low resistance resolution; a second resistance element having a length equal to a minor fraction of that of said first resistance element and having a relatively high resistance resolution; and a contact assembly including a first contact element movable over the length of said first resistance element and a plurality of second contact elements electrically directly interconnected and simultaneously successively movable over said second resistance element, said contact elements being eifective to connect said resistance elements in series, whereby the apparatus has an effective resolution over its entire range of values equal to that of said second resistance element.

2. Apparatus for providing a continuously variable resistance over a Wide range of values comprising: an elongated first resistance element including a plurality of serially-connected sections and a plurality of contact elements connected to the junctions thereof; a second resistance element having a length equal to a minor fraction of that of said first resistance element and having'a relatively high resistance resolution; and a contact assembly including a first contact element movable over the contact elements of said first resistance element and a plurality of second contact elements electrically directly interconnected and simultaneously successively movable over said second resistance element, said contact elements being efiective to connect said resistance elements in series, whereby the apparatus has an effective resolution over its entire range of values equal to that of said second resistance element.

3. Apparatus for providing a continuously variable resistance over a wide range of values comprising: an elongated first resistance element including a plurality of serially-connected sections and a plurality of contact elements connected to the junctions thereof; a second resistance element having a length substantially equal to the distance between adjacent ones of said contact elements and having a relatively high resistance resolution; and a contact assembly including a first contact element movable over the contact elements of said first resistance element and a plurality of second contact elements electrically directly interconnected and simultaneously successively movable over said second resistance element, said contact elements being effective to connect said resistance elements in series, whereby the apparatus has an effective resolution over its entire range of values equal to that of said second resistance element.

4. Apparatus for providing a continuously variable resistance over a wide range of values comprising: an elongated first resistance element having a relatively low resistance resolution; a second resistance element having a length equal to a minor fraction of that of said first resistance element and a resistance value equal to the resistance resolution of said first resistance element and having a relatively high resistance resolution; and a contact assembly including a first contact element movable over the length ofsaid first resistance element and a plurality of second contact elements electricallydirectly being effective to connect said resistance elements in series, whereby the apparatus has an effective resolution over its entire range of values equal to that of said second resistance element.

5. Apparatus for providing a continuously variable resistance over a wide range of values comprising: a circular wound-wire first resistance element having a relatively low resistance resolution; a circular segmental wound-wire second resistance element concentric with said first resistance element and having a length equal to a minor fraction of that of said first resistance element and having a relatively high resistanc resolution; and a contact assembly relatively rotatable with respect to said resistance elements and including a first contact element movable over the length of said first resistance element and a plurality of second contact elements electrically interconnected and simultaneously successively movable over said second resistance element, said contact elements being effective to connect said resistance elements in series, whereby the apparatus has an effective resolution over its entire range of values equal to that of said second resistance element.

6. Apparatus for providing a continuously variable resistance over a wide range of values comprising: an elongated wound-wire first resistance element having a relatively low resistance resolution; a wound-wire second resistance element having an over-all length mechanically equal to that of said first resistance element but an electrically effective length equal to a minor fraction of that of said first resistance element and having a relatively high resistance resolution; and a contact assembly including a first contact element movable over the length of said first resistance element and a plurality of second contact elements electrically directly interconnected and simultaneously successively movable over said second resistance element, said contact elements being effective to connect said resistance elements in series, whereby the apparatus has an effective resolution over its entire range of values equal to that of said second resistance element.

7. Apparatus for providing a continuously variable resistance over a wide range of values comprising: an elongated first resistance element having a relatively low resistance resolution; a second resistance element having a length equal to a minor fraction of that of said first resistance element and having a relatively high resistance resolution; and a contact assembly including a first contact element movable over the length of said first resistance element and a plurality of second contact elements electrically directly interconnected and simultaneously successively movable over said second resistance element, all of said contact elements being electrically interconnected and eifective to connect said resistance elements in series without auxiliary sliding contacts, whereby the apparatus has an effective resolution over its entire range of values equal to that of said second resistance element.

References Cited in the tile of this patent UNITED STATES PATENTS 

